1. Field of the Invention
The present invention relates to an agglomerating process and an apparatus therefor of iron ore sinter mix to be supplied to a Dwight-Lloyd continuous sintering machine, and in particular, to the technology of the steps in which the raw feed for sintering preparation is mixed and kneaded with vibrating media and then agglomerated by tumbling.
2. Description of the Conventional Technology
According to the conventional technology, the raw feed for sintering preparation (fine powdery stone, limestone, fine coke, quicklime, and fine return cake, etc.) contained in the storage bins for blending of the raw feed is supplied at desired quantities by a constant feeder situated at the lower portion of the storage bins onto a belt conveyor, heaping multilayers. The raw feed is added with water to make water content of 5 to 7 weight % and is blended and agglomerated into sinter mix in a drum mixer. The sinter mix is transferred to a sinter supply hopper and is charged onto pallets of the sintering machine through a drum feeder and a sinter supply chute, respectively placed on the lower part of the hopper. Then, fine coke in the sinter mix is ignited by an ignition burner and sintering operation proceeds.
In the case above, fine powdery iron ore having particles of grain size less than 63 .mu.m (undersize particle screened by the minimum sieve defined in Japanese Industrial Standard Z8801) of more than 60 weight % is also used.
There are troubles in the conventional sintering process. That is, when fine powdery iron ore of more than 10 weight % is contaied in the sinter mix, permeability through the sintering bed is prohibited and the sintering productivity decreases. It is accordingly necessary to add much binders (quicklime, slaked lime and the like) in the sinter mix to improve permeability, increasing cost of binders.
In order to solve the shortcomings above of the conventional art, the fine powdery iron ore of about 60 weight % and the nuclei composed of fine return cake or iron ore of about 40 weight % are previously agglomerated in a drum mixer or disc pelletizer, the agglomerated material is blended with the other raw feed for sintering preparation, and the blend is charged to the drum mixer to be mixed and agglomerated.
The nuclei agglomeration or granulation method of fine powdery iron ore is described in "The Journal of The Iron and Steel Institute of Japan", vol. 71, No. 10 (1985), entitled "Granulation of sinter feed and its role in sintering." In this case, it is necessary to use nuclei and therefore the required capacity of the mixer must be 1.4 times of that of the ordinary mixer as the same fine powdery iron composition, disadvantageously rising the cost of installation.
According to other granulation method, a fine iron ore of up to about 40 weight % is blended with 60 weight % of ordinary iron ore raw feed and the blend is supplied to the disc pelletizer, in which the blend is agglomerated into green pellets of 5 to 10 mm in diameter. Then fine powdery coke is added to cover outer surfaces of the green pellets, and the covered pellets are transferred to the sinter supply hopper for sintering. The conventional method above is described in "The Journal of The Iron and Steel Institute of Japan", vol. 73, No. 11 (1987), entitled "Fundamental Investigation on Production Conditions of New Iron Ore Agglomerates for Blast Furnace Burdens and Evaluation of Their Properties."
According to the shortcomings of the conventional method above, the bulk density of a green ball is low and the crushing strength of the ball is low, so that the ball is friable in the course of transferring to the sintering bed, inhibiting the permeability of the sintering bed. It is disadvantageously necessary that the mean grain size of the green pellets must be so large as 8 to 10 mm and the pellets must be covered with carbon. When the outer-clad coke does not be adhered uniformly to the outer surfaces of the green pellets, the inner portion of the balls may not melt and the balls may disassemble to a single pellet or become to fine return cakes in the crushing stage of the sintered products.
According to the other conventional agglomerating method using a wet grinding mixer described in Japanese Patent publication Sho 43(1968)-6256, the raw feed for sintering preparation is ground, controlled in water content, mixed in the wet grinding mixer such as a ball mill or a rod mill, then the blend is agglomerated into green pellets through a vertical-type, or cylindrical-type, or other agglomerator.
According to the conventional agglomerating method above, a step of dry or wet grinding operation and another step of water-controlling mixing operation are done in a rotating rod mill or a ball mill. The installation is relatively too large to the yield, necessisating vast power consumption and too much expenses.